1. Field of the Invention
The invention relates to an image sensor, and more particularly to an image sensor with a disconnected color filter structure and fabrication method thereof.
2. Description of the Related Art
An image sensor, as a kind of semiconductor device, transforms optical images into electrical signals. Image sensors can be generally classified into charge coupled devices (CCDs) and complementary metal oxide semiconductor (CMOS) image sensors. Among these image sensors, a CMOS image sensor comprises a photodiode for detecting incident light and transforming it into electrical signals, and logic circuits for transmitting and processing the electrical signals.
A conventional method for manufacturing a CMOS image sensor comprising microlenses is hereinafter described referring to FIGS. 1A to 1C.
First, referring to FIG. 1C, a conventional CMOS image sensor is provided. The CMOS image sensor comprises a light sensing part 13 comprising a photodiode 11 for accepting incident light, and for generating and accumulating electric charges, a protecting layer 21 formed on a structure of the light sensing part 13, a color filter array 23, and a plurality of microlenses 27.
In a conventional method of manufacturing such a structured CMOS image sensor, as shown in FIG. 1A, the protecting layer 21 with a silicon nitride base is formed on a semiconductor substrate 10 that comprises the light sensing part 13 comprising the photodiodes 11. Then, as shown in FIG. 1B, the color filter array 23 (with a connected color filter structure) is formed on the protecting layer 21. Here, the color filter array 23 is formed in a primary color system, i.e., comprising a red filter (R), a green filter (G), and a blue filter (B), using photoresist materials containing a red, green, or blue pigment, respectively. Formation of each color filter involves a series of coating, exposure and development processes according to photolithography techniques. Alternatively, the color filter array 23 can be formed in a complementary color system comprising cyan, yellow, and magenta filters.
Then, as shown in FIG. 1C, a photoresist layer is applied, exposed, and developed on the color filter array 23; thus forming a plurality of photoresist patterns. These photoresist patterns are then thermally reflowed and cured to form lenses; thus resulting in a plurality of microlenses 27.
According to the conventional method, the microlenses 27 are formed with a distant from each other by about 0.2 μm to 0.5 μm (due to the connected color filter structure), for the purpose of preventing formation of bridges between the microlenses 27 during the curing and reflowing processes of corresponding photoresist patterns. However, a gap between the microlenses 27 results, such that at least some light incident between the microlenses 27 is loss, and resolution of color signals may be decreased to a level that is less than optimal due to oblique light incident to adjacent pixels.
Additionally, the microlenses 27 are formed by a coating, photolithography and thermal process. Thus, the materials of the microlenses 27 are limited to only photo type materials.